Generally, a battery is assembled by a negative electrode, a positive electrode, and a separator interposed therebetween. Here, the separator positioned between the two electrodes of the battery is a subsidiary material which prevents the negative electrode and the positive electrode from being in direct contact with each other to prevent an internal short-circuit, and plays an important role not only as an ion passage in the battery but also in improving the safety of the battery.
FIG. 1 is a view showing a general structure of a zinc-air battery.
The zinc-air battery includes a positive electrode, a separator 40, an electrolyte 50 and a negative electrode.
First, the positive electrode includes a carbon layer 20, a positive electrode current collector 30 in a metal mesh form formed in the interior of the carbon layer 20, and a Teflon layer 10 formed on the upper part of the carbon layer 20.
Further, the separator 40 is disposed at the lower part of the carbon layer 20, and a negative electrode current collector 60 of the negative electrode is formed apart from the separator 40 at a predetermined distance.
The electrolyte 50 is formed as a slurry in which zinc (Zn), potassium hydroxide (KOH) and water (H2O) are mixed, and accommodated between the separator 40 and the negative electrode current collector 60. Here, the electrolyte 50 passes through the separator 40 capable of selective ion migration and impregnates a part of the carbon layer 20 to form a gas-liquid interface 21.
The zinc-air battery formed as above operates by the migration of electrons generated when zinc contained in the electrolyte 50 reacts with oxygen in the air and is changed into zinc oxide.
In the conventional zinc-air battery as described above, the electrolyte 50 impregnates a part of the carbon layer 20 through a plurality of pores of the separator 40, and potassium hydroxide contained in the electrolyte 50 reacts with oxygen in the air and is precipitated. As a result, the carbon layer 20 is destroyed and the performance of the zinc-air battery is deteriorated.
Further, when the zinc-air battery is charged, oxygen migrates to the positive electrode side, and the oxygen migrated to the positive electrode side reacts with potassium hydroxide such that potassium hydroxide is precipitated, and thus it is difficult to use the zinc-air battery as a secondary battery.
The present invention is designed to solve the aforementioned problems, and it is an object of the present invention to provide a separator capable of selective ion migration in which each of a plurality of pores of a porous ion migration inhibition layer is formed so as to have a size smaller than the size of an electromigration-promoting ion contained in an electrolyte, and thus the electromigration-promoting ion is prevented from passing through the porous ion migration inhibition layer, and a secondary battery including the same.
According to an aspect of the present invention, there is provided a separator capable of selective ion migration, including: a support formed in a grid; and a porous ion migration inhibition layer with which the grid of the support is coated and which has a plurality of pores formed therein, where each of the plurality of pores of the porous ion migration inhibition layer is formed so as to have a size smaller than the size of an electromigration-promoting ion contained in an electrolyte, and thus the electromigration-promoting ion is prevented from passing through the porous ion migration inhibition layer.
Here, the support may be formed of polyvinyl alcohol (PVA), and the porous ion migration inhibition layer is formed of polyvinyl acetate (PVAc).
The porous ion migration inhibition layer may be formed by an electrospinning process of electrically charging polyvinyl acetate (PVAc) and spinning the polyvinyl acetate (PVAc) onto the support.
Further, the porous ion migration inhibition layer may be formed by substituting polyvinyl acetate (PVAc) with at least one alkali metal or alkaline earth metal.
Further, according to another aspect of the present invention, there is provided a secondary battery, including: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte for partially impregnating the negative electrode, the separator and the positive electrode, where the separator is formed of a porous material having a plurality of pores formed therein, and each of the plurality of pores of the porous ion migration inhibition layer is formed so as to have a size smaller than the size of an electromigration-promoting ion contained in an electrolyte, and thus the electromigration-promoting ion is prevented from passing through the porous ion migration inhibition layer and migrating to the positive electrode side.
Accordingly, the present invention has the following effects.
First, the performance of a zinc-air battery can be prevented from being degraded in a manner whereby a plurality of pores in the porous ion migration inhibition layer of the separator are formed so as to have a size smaller than the size of potassium ions contained in an electrolyte, thereby preventing the potassium ions from migrating to a carbon layer to fundamentally prevent potassium hydroxide from being precipitated, whereby the carbon layer is destroyed.
Second, a zinc-air battery can be used as a secondary battery in a manner whereby potassium is prevented from migrating to the carbon layer, thereby preventing potassium hydroxide from being precipitated even when oxygen is moved to a positive electrode side during charging of the zinc-air battery.
Third, when the present invention is applied to a separator of an alkaline battery, it is possible to prevent potassium hydroxide from being precipitated during charging, thereby achieving an effect that an alkaline primary battery can be used as a secondary battery.